{
0
:
{associate_sales: "j72LOAjajLRbKKK0XYfHcCMghdB3", displayName: "Sneh", email: "sneh@email.com",  timespan: 1, …}
1
:
{displayName: " Sales4", email: "sales4@email.com",  timespan: 1, uid: "2e5piC6E8eO16qDDaP0qPA0LDRJ3", …}
2
:
{associate_sales: "c8kMXIkXcRgTUInPbdhL5oinbzv2", displayName: " client11", email: "client11@email.com", timespan: 12, …}
3
:
{associate_sales: "j72LOAjajLRbKKK0XYfHcCMghdB3", displayName: "Client1", email: "client1@email.com", timespan: 1522320931451, …} }

this.databaseObj2.orderByChild('timespan').once('value', (snapshot) => {
// code
});